Cell Biology Test 3

kinesins

a large family of motor proteins that uses energy of ATP hydrolysis to move toward the plus end of a microtubule.

F-actin

filament actin made of 45kDalton protein

4 classes of intermediate filaments

1) keratin filaments (in epithelial cells) epithelial - type 1 keratin and type 2 keratin (found in epithelial cells and derivatives like hair and nails) 2)vimentin and vimentin related filaments (in connective-tissue cells, muscle cells and supporting cells of the nervous system) 3)neurofilaments in nerve cells 4) nuclear lamins A, B, and C (to strengthen the nuclear envelope and nuclear lamina)

steps in cell crawling (protrusion, adhesion, traction, tail retraction)

1)protrusion extending the cell by the polyermization of actin filaments 2)attachement 3)traction 4)retraction (contraction) - myosin helps at the back end to interact with actin to squeeze and push the back end of the cell forward.

sarcomeres

highly organized assemblies of actin filaments (thin) and myosin II filaments (thick) to form the basic muscle structure. myosin II and actin filaments interaction takes place when skeletal muscles receive a signal from a motor nerve. Z disc is boundary of the sarcomere, adjacent to other sarcomeres. A region/band is there actin and myosin overlap. I band is where myosin extends past actin. For contraction, the myosin heads walk toward the plus end of actin (opposite from one another) to pull the actin closer together.

critical concentration

if monomer (actin) concentration is too low, there will not be any assembly of subunits so there will actually be a slight shrinking. Above the critical concentration there is growth. Below the critical concentration there is shrinking. AT the critical concentration there is neither. when capping proteins are present the slope of the critical concentration graph is not as steep as normal because there is only growth at the minus end. at 0 there is no growth or shrinking. above the 0 line there and growth. below the 0 line there is shrinking. values on the Y-axis show the rate of growth or shrinking.

centriole

important structure for organizing microtubules for cell division. made of 9 groups of microtubules which are each composed of triplets. microtubules don't extend directly form the triplets but rather the surrounding region. centrioles are separated during the end of G1 and duplicated during S phase. in an experiment, when a cell was severed, the severed fragment without a nucleus or centrosome or centrioles was still able to develop with its own microtubule organizing center.

phragmoplast

in a dividing plant cell, structure made of microtubules and membrane vesicles that guides the formation of a new cell wall.

3 classes of filaments in the cytoskeleton

intermediate filaments (10nm diameter, made of intermediate filament proteins) microtubules (25nm, made of tubulin dimers) actin filaments (7nm, made of actin protein)

microtubule organizing center (MTOC)

is a structure found in eukaryotic cells from which microtubules emerge. MTOCs have two main functions: the organization of eukaryotic flagella and cilia and the organization of the mitotic and meiotic spindle apparatus

motor proteins

protein such as myosin or kinesin that uses energy derived from ATP hydrolysis to propel itself along a protein filament or polymeric molecule. Motor proteins drive saltatory movements (jerky steps - moving for a short period of time, stopping moving again)

tropomyosin

protein that blocks actin/myosin interaction tropomyosin bind to actin (in the region where myosin would normally bind). once Ca++ is released into the cytosol it releases tropomyosin to allow myosin to interact with actin stabilizes filament by binding along the side of actin in a parallel fashion.

sarcolemma

refers to plasma membrane of muscle cell

ERM proteins (Ezrin, Radixin, Moesin)

regulated proteins that can bind to actin and the plasma membrane proteins. ERM proteins are only sometimes turned on. ERM proteins begin in an unactivated state. they receive signals (phosphorylation or PIP2 binding) which converts them to an activated and extended conformation. ERM proteins the bind to actin on one end and a transmembrane protein on the other end.

terminal web

the base of the microvilli structure where the is a cross-linking of actin filaments.

axoneme

the central strand of a cilium or flagellum. It is composed of an array of microtubules, typically in nine pairs around two single central ones. when flagella is separated in a test tube we can see that there is a plus end and a minus end

dynamic instability

the property that microtubules can shrink and grow form the plus end rapidly and continuously.

troponin complex

The C subunit of the troponin complex interacts with the Ca++ released to change the conformation of tropomyosin to then allow myosin to interact with actin for muscle contraction

Clare Waterman (speckle microscopy)

To prove the treadmill theory, waterman was studying tubulin dimers with a fluorescent tag. They saw that the whole microtubules would light up. Then Wateman started adding a much lower concentration of microtubules at a time. This allowed "speckles" to appear. The speckles can be used to saw whether or not the microtubule is moving as a whole or treadmilling. The process asks the question: does the speckle move with the microtubule as a whole or is it treadmilling? Speckles are a way to track microtubules.

cofilin

binds ADP-actin filaments, accelerates disassembly. actin and cofilin causes super twisting and disassembly from the back edge of lamellipodium movement.

polarity in actin filaments

both ends of actin can have monomers attached but the plus end grows much faster than the minus end.

lamellipodia and filopodia

both extend their actin filaments toward the plasma membrane to help the cell move forward, touch down on a favorable surface and stick. both lamellipodia and filopodia are exploratory, motile structures that form and retract with great speed, moving at around 1 um per second. both are thought to be generated by the rapid local growth of actin filaments, which assemble close to the plasma membrane and elongate by the addition of actin monomers at their plus ends. the leading edge of a crawling fibroblast in culture regularly extends thin sheet-like lamellipodia, which contain a dense meshowkr of actin filaments, oriented to that most of the filaments have their plus end close to the plasma membrane. many cells also extend thin, stiff protrusions called filopodia, both at the leading edge and else where on their surface. filopodia depend on formins which are nucleating proteins that attach to the growing plus end of actin and promote polymerization.

tropomodulin

capping protein on minus end of actin filament in sarcomeres.

rigor mortis

caused by chemical changes in the muscles post mortem, which cause the limbs of the corpse to stiffen

power stroke cycle of actin-myosin

cilia move with the power stoke movement. myosin II has a 5 to 10 nm swing of lever arm. myosin V has a 30 to 40nm swing of lever arm, therefore it is faster moving than myosin II. both move toward the plus end of actin filaments. The head attached to the actin.

Tim Mitchison/Mark Kirschner

coined the term dynamic instability.

severing proteins

cut actin filaments in the middle. The critical concentration line is much steeper (than normal) when severing proteins are present because there are more nucleation sites to bind to for growth. When severing proteins are present actin filaments grow and shrink more rapidly. Gelsolin can bind to actin filaments and severe them. Gelsolin then acts as a cap on the actin. severs filaments and binds to plus end.

epidermolysis bullosa simplex (EBS)

disease related to keratin mutation when the cells fold and cant properly hold their shape and fold causing skin ailments. in which mutations in the keratin genes interfere with the formation of keratin filaments in the epidermis. As a result, the skin is highly vulnerable to mechanical injury and even a gentle pressure can rupture its cells, causing the skin to blister. there is incorrect intermediate filament structure holding the basal cell of epidermis to the basal lamina

cytochalasin B

drug that affect actin filaments : caps filament plus end, preventing polymerization there.

latrunculin A

drug that affects actin filaments : binds actin monomers and prevents their polymerization

cilia

hairlike structures made of microtubules found on the surface of many eukaryotic cells; when present in large number, its rhythmic beating can drive the movement of fluid over the cell surface, as in the epithelium of the lungs. They can also move to propel single cells through a fluid.

tubulin

heterodimer composed of two globular proteins (alpha and beta) bound together with noncovalent interactions. The dimers stack with noncovalent bonds to form the walls of the tubulins, 13 parallel protofilaments at the top looking down the tube (with alpha at the minus end and beta at the plus end which give the whole microtubule a polarity). 13 dimers form microtubule. tubulin dimers are added more rapidly at the plus end rather than the minus end when forming microtubules.

Arp2/3

Arp complex provides start site for actin. this complex serves at nucleation site for actin filaments. inactive ARP complex interacting with an activating factor to allow the minus end of the actin filament to develop. ARP2/3 complex helps actin for a branched structure with 70 degree angles. nucleates assembly to form a web and remains associated with the minus end.

gelosin and wound healing interaction

there are normally actin filaments capped in unactivated blood platelet (cells that circulate in the blood) but when its is activated by Ca++ there is an influx of gelsolin. The actin is the severed and capped by the activated-Ca++ gelsolin. there is eventually a signal to reduce gelsolin and there is rapid actin filament growth from the previous short actin filaments. then there is bundling and cross-linking of actin filaments and myosin contraction to allow the activated platelet spread out and attached to blood clots.

G-actin

globular actin made of 45kDalton protein

neurofilaments

Neurofilaments (NF) are the 10 nanometer or intermediate filaments found in neurons. They are a major component of the neuronal cytoskeleton, and are believed to function primarily to provide structural support for the axon and to regulate axon diameter. intermediate filaments in nerve cells

Ca++ release for contraction

T tubule has a voltage-gated calcium channel (AKA : dihydropyridine receptor) non activated muscle cell, the gate is closed. When there is an action potential, the gate opens and calcium is released. Oe the sarcoplasmic reticulum there is a calcium-gated calcium channel (AKA: ryanodine receptor). The small amount of calcium released from the voltage-gated calcium channel binds to this second channel to release more calcium into the cytosol. The Ca++ is used to interact with the C region of the troponin complex to allow actin-myosin interaction. Ca++ alters the conformation of troponin to cause tropomyosin to alters it position and allows myosin heads to interact with actin filaments.

monomer-binding proteins

Type 1: profilin which binds to monomer and promotes assembly. Monomers in the presence of profilin experience rapid rates of growth at the plus end and increase rate of assembly. Binds subunits, speeds elongation. Type 2: thymosin acts like a sponge and prevents monomer assembly and doesn't even bind to the actin. binds subunits, prevents assembly. Profilin competes with thymosin for binding to actin monomers.

taxol

a drug produced by YEW (a tree) taxol promotes assembly of microtubules. Used in clinical settings. microtubule-specific drug that binds and stabilizes microtubules

muscle contraction

a rise in Ca2+ levels in the cytosol cause tropomyosin molecules and troponin molecules to alter positions and allows myosin heads to bind to the actin filaments, initiating contraction. 1) myosin head begin attached to actin filament. 2)ATP binds to myosin head which reduces the affinity of the head for actin and releases the head from the actin filament. 3) the myosin head is slightly displaced from the actin. The ATP is hydrolyzed but both ADP and the phosphate remain attached to the myosin head. 4) the phosphate is removed from the head which allows the myosin head to regain interaction with the myosin. 5) the ADP is the removed which allows the myosin head to return to its original shape.

microtubule-associated proteins

accessory protein that binds to microtubules; can stabilize microtubule filaments, link them to other cell structures, or transport various components along their length.

contractile ring

actin and myosin interacting at the equator of the cell to help it divide The contractile ring (actin and myosin filaments) carries out cytoplasmic division (cytokinesis). The mitotic apparatus dictates the location of the contractile ring.

Listeria monocytogenes

bacteria that causes the infection listeriosis this is a bacteria that binds to actin similarly to the ARP complex and as actin polymerizes it pushes the bacteria through a cell without being detected by the cell's immune system. the free bacterium enters the host cell and there is actin nucleation on one end of the bacteria which propels the bacteria forward. the bacteria can then push through to other host cells. to do this, the bacteria has an ActA molecule that binds to the ARP complex which causes actin nucleation.

polymerization of actin

actin filaments are made of actin monomers. free actin monomers have a cleft for the attachment of ATP or ADP . they carry a tightly bound ATP to hydrolyze to ADP soon after it is incorporated into the filament. dimers bind and form a double helix structure with a plus and minus end. when the concentration of free actin filaments is high, monomers are added to both ends. However when the concentration of free actin filaments is at an intermediate, the minus side loses monomers while the plus side continues to receive additional monomers. formins and actin-related proteins (ARPs) promote actin polymerization

actin nucleation

actin polymerizes very similarly to microtubules. monomers are added at both end, but more rapidly at the plus end. free actin monomers carry a tightly bound ATP. the actin monomer hydrolyzes its bound ATP to ADP soon after it is incorporated into the filament. the hydrolysis of ATP to ADP reduces the strength of binding between the monomers thereby decreasing the stability of the polymer.

plectin

acts to crosslink intermediate filaments with microtubules this is important because it shoes that there can be interaction between cytoskeletal elements.

Rho, Rac, CDC42

all with the Ras family of proteins that function in the modulation. The are important for modification to the structure of the cytoplasm. Rho - stress fiber formation. microinjection of an activated form of Rho promotes the rapid assembly of bundles of long, unbranched actin filaments; because myosin is associated with these bundles, they are contractile. These techniques have revealed that Rho regulates the myosin light chain phosphatase Rac - lamellipodia. microinjection of an activated form of Rac, a GTP-binding protein similar to Rho, causes the formation of an enormous lamellipodium that extends from the entire circumference of the cell. CDC42 - filopodia. microinjection of an activated form of Cdc42, another Rho family member, stimulates the protrusion of many long filopodia at the cell periphery.

phalloidin

an actin-specific drug that binds and stabilizes filaments.

cytoskeleton

an intricate network of protein filaments that extends throughout the cytoplasm. It helps support the large volume of cytoplasm. Mostly prominent in eukaryotic cells. It is highly dynamic and continuously reorganized as the cell changes shape, divides and responds to its environment. It also controls the locations of organelles and provides machinery for transport between them

process of elongating microtubules

as alpha/beta tubulin is added to form a growing microtubule, GTP binds and is hydrolyzed. While growth is occurring tubulin-bound GTP is added more rapidly than it can be hydrolyzed which creates a GTP cap, helping to hold dimers together more strongly. Once this cap is lost, the microtubule will rapidly dissociate. During mitosis, cells switch between growing and shrinking of their microtubules much more frequently than during their regular interphase.

sliding filament model of contraction

as the myosin heads pull actin filaments together as they move toward the plus end of actin. the actin and myosin filaments of a sarcomere overlap with the same relative polarity on either side of the midline. actin filaments are anchored by their plus end to the Z disc. during contraction, the actin and myosin filaments slide past each other without shortening. this sliding motion is driven by the myosin heads walking toward the plus end of the adjacent actin filaments. myosin begins attached to the actin filament. ATP then binds to myosin which releases the myosin head from the actin filament. There is a cocking step where the ATP is hydrolyzed to ADP which swings the myosin head forward. The phosphate is them removed to attach the myosin back to the actin filament. Finally, once ADP is removed from the myosin head, the original shape returns.

capping proteins

at the plus end, prevents growth at the plus end so only growth occurs slowly at the minus end. capping proteins stabilize the interaction between the centrosome and the plasma membrane prevents assembly and disassembly at plus end of actin.

alpha, beta, gamma tubulins

gamma tubulin ring complex: gamma tubulin acts as nucleating site (similar to Arp in actin). The minus end is bound to gamma tubulin ring complex which is known as TURK

cross-linking proteins (alpha-actinin, fimbrin, filamin, villin, spactrin)

each part of the cell relied on different orientations of cross-linking based on its function. actin filament orientation can occur as: contractile bundles, gel-like networks, or tight parallel bundles. Alpha-actinin: cross linking protein to bundle actin. each end of the monomer has a binding site. This creates more spacing between actin. Present in contractile bundles and loose packing allows myosin 2 to enter bundle. Helps alongside fimbrin during blood platelet work. Fimbrin: can hold actin in tight bundles, similar to alpha Actinin but at closer compaction. This tight packing prevents myosin 2 from entering bundle. helps during blood platelet work. Filamin: seen in gel-like cross linking. protein that holds two filaments in a criss-cross orientation. Villin: contributes to microvilli organization at the tip of the microvilli Spectrin: holds actin apart. Found in red blood cells. spectin is also involved in binding microtubules to dynein to dynactin complex to vesicles.

Titin

elastic protein attached to myosin to help it in the middle. bound to the end of myosin at one end and the Z disc at the other.

microtubules

extend out form the centromere as stiff hollow tubes that create a system of tracks. They can form the mitotic spindle for mitosis. They can form cilia and flagella and hairlike structure that extend from the surface of many eukaryotes. they are the part of the cytoskeleton mainly responsible for transporting and positioning membrane-enclosed organelles within the cell and for guiding the intracellular transport of various cytosolic macromolecules. when a cell enters mitosis the cytoplasmic microtubules disassemble and reassemble into an intricate structure called the mitotic spindle. Tubulin protein molecules make up microtubules. 25nm In nondividing cells microtubules extend form the centromere. In dividing cells they extend form each of the microtubules and their overlap region instructs the region for the contractile ring. In ciliated cells, microtubules extend from the basal bodies into the cilium.

Rho family

family of small, monomeric GTPases that control the organization of the actin cytoskeleton. They function as molecular switches. GTP-bound in an active state and GDP-bound in an inactive state. in the case of the cytoskeleton, activation of different members of the Rho family affects the organization of actin filaments in different ways.

transverse tubule system (T-tubules)

formed of muscle cells from invaginations of plasma membrane. are extensions of the cell membrane that penetrate into the centre of skeletal and cardiac muscle cells

nuclear lamina

forms a 20 meshwork lining and strengthening the inside surface of the inner nuclear membrane. Lamina are made up of lamin proteins. The lamina is disassembled (phosphorylation) and assembled (dephosphorylation) with each round of mitosis. nuclear lamins are the most dynamic of the types of intermediate filaments (most of the rest are very stable). They are located just outside the nuclear envelope and they provide structure.

keratin filaments

found in epithelial cells. formed from a mixture of keratin subunits. these filaments span the interiors of epithelial cells one end to the other and are indirectly connected through desmosomes . the ends of keratin filaments are anchored to the desmosomes, and the filaments associate laterally with other cell components through the globular head and tail domains that project from their surface. accessory proteins called plectin stabilize and reinforce by linking microtubules to intermediate filaments. mutations of plectin can be fatal. EBS is a disease related to keratin mutation

lag phase, elongation phase, steady-state equilibrium of actin

lag phase: low concentration of subunits in filaments. there is a lag time at the first nucleation site. elongation (growth phase): rapid increase of actin filaments forming from subunits steady state: when the concentration of monomers available matches with the concentration of subunits in filaments and the rate of monomer coming off the actin is the same rate on both the plus and minus ends. when preformed filament seeds are added there is no lag time. if the concentration of free actin monomers is very high, an actin filament will grow rapidly. treadmilling occurs at an intermediate concentration.

flagella

long, whiplike structures capable of propelling a cell through a fluid medium with its rhythmic beating. eukaryotic flagella are longer versions of cilia; bacterial flagella are completely different, being smaller and simpler in construction. They are designed to move an entire cell (rather than just fluid around). Linking proteins and ATP are necessary for their proper functioning and swimming motion. two types of microtubules and dynein join to form the flagellum structure: B microtubule bound to A microtubule. there are nine of these combination bound to outer dynein arm and an inner dynein arm. Nexin holds each of the nine together surrounding two central microtubules.

myofibrils

make up the contractile elements of muscle cells in the cytoplasm. Myofibrils are made of chains of tiny contractile units called sarcomeres.

actin-binding protein

many types of proteins that interacts with actin monomers or filaments to control the assembly, structure and behavior of actin filaments and networks. They often bind to the assembled filament and control its behavior. nucleating proteins, bundling proteins, myosin motor proteins, side-binding proteins, capping (plus-end-blocking) protein, cross-linking protein, severing protein

yeast mating/shmoo

mating between a and alpha types of budding yeast where one cell extends toward the other cell, the shape is known as shmoo. Each type of yeast has a specific receptor for the other type. A mating factor binds to the mating factor receptor. A G protein is then activated by GDP causing Cdc42 to activate which causes Rho and formin to encourage actin filament polymerization. This helps the front end of the yeast cell to protrude forward toward the other cell. a similar actin process occurs with neutrophils who have receptors for bacteria and polymerize actin to move in its direction.

intermediate filaments

mechanical strength enables cells to withstand the mechanical stress that occurs when cells are stretched toughest and most durable of the cytoskeletal filaments, rope-like. found in large numbers in the cytoplasm and also found in the nucleus. surrounds the nucleus and extends outward where they often anchor to desmosomes on the plasma membrane they form a meshwork called nuclear lamina to strengthen the nuclear envelope and surround chromatin. the intermediate filaments of the nuclear lamina line the inner face of the nuclear envelope and are thought to provide attachment sites from the chromosomes. they don't have a polarity to they don't have associated motor proteins because the proteins wouldn't know which way to walk. 10nm. made of fibrous intermediate filament proteins.

centrosome

microtubule-organizing center that sits near the nucleus in an animal cell. During the cell cycle, this structure duplicates to form the two poles of the mitotic spindle. The centrosome contains a pair of centrioles: cylindrical array of microtubules usually found in pairs at the center of a chromosome in animal cells. Also found at the base of cilia and flagella, where they are the basal bodies. the centrosome matrix contain a special type of tubulin, y-tubulin, that provides the starting point when the minus end of microtubules beginning with the plus end growing and elongating into the cytoplasm. In most cells, the centrosome has a tethering and association with the nucleus. When a cell is severed, it will eventually reorganize around a new centrosome (even if this new centrosome doesn't have centrioles).

colchicime

microtubule-specific drug that binds tubulin dimers and prevents their polymerization.

vinblastine/vincristine

microtubule-specific drug that binds tubulin dimers and prevents their polymerization.

microvilli structure

microvilli have long extensions with actin in tightly packed parallel structure and at the bottom of the microvilli is the terminal web which is made of many cross-linking proteins to form the root base for the microvilli. The tips of the microvilli have the plus end of actin filaments and through the entire structure are cross-linking villin and fimbrin proteins for organization. Myosin 1 and calmodulin line the inner structure plasma membrane. microvilli extend from epithelial cells in the gut microvilli with tight bundles of actin. Villin contributes to this organization. The terminal web acts as the roots (made of cross-linked actin filaments)

gamma TURK

minus end of microtubules bound to the nucleating site of gamma tubulin around centrioles. nucleates assembly of microtubules and remains associated with the minus end

dynein

motor protein that uses the energy of ATP hydrolysis to move toward the minus end of a microtubule. One form of the protein is responsible for the bending of cilia. dynein and kinesins are important in axons of neurons because they help carry vesicles with signal back and forth.

ATP-binding domain/actin binding domain

myosin I molecules have a head domain and a tail. the head domain binds to an actin filament and has the ATP-hydrolyzing motor activity that enables it to move along the filament in a repetitive cycle of binding, detachment, and rebinding. The tail varies among the different types of myosin-I and determines what type of cargo the myosin drags along.

Ras superfamily

oncogene, GTP-binding proteins

myosin light chain kinase (MLCK)

phosphorylates ATP to change the conformation in the inactive form, myosin's tail end is slightly wrapped. ATP is used to phosphorylate the light chain of myosin which extends the orientation of the tail region. This process allows for the spontaneous assembly of bipolar myosin filaments.

Nitella/in vitro actin-myosin motility assays

photosynthetic There are actin filaments parallel to the long axis of these tubes which allows chloroplasts to move throughout. When a chloroplast is added to exposed cell wall there is no movement but when ATP is also added, chloroplast movement resumes. This study helps understand myosin and actin interaction with ATP and rates of movement. This was am important system for studying interaction.

cap Z

plus end capping protein on actin filament in sarcomere. Located at the Z disc of sarcomeres.

microtubule plus vs minus end

polymerization with GTP followed by nucleoside hydrolysis to leave GDP bound to the polymer. The GDP is weaker so it will eventually depolymerize (unless there is a GTP cap) the minus end is alpha tubulin of the dimer. fast addition of dimers and hydrolysis lags behind the plus end is beta tubulin of the dimer. addition is low and hydrolysis catches up.

Progeria and Sam Bern's story

premature aging rare disease that causes reduced life expectancy due to things often associated with problems of older age. normal cells have a round nucleus but the nucleus of progeria disease is mutated is unorganized and folded. children with progeria have wrinkled skin, lose their teeth and hair. nuclear instability that leads to impaired cell division. In the case of Sam, his parents got help from Francis Collins. They figured out that is was a defect in the nuclear lamin. This is caused by how lamin A is processed. The CoCH3 (hydrophobic) helps tether the protein to the cytosol. Normally lamin A is then released into the nucleus by a protesase. The mutation splices RSYLLG which prevents the lamin A from being cut by the protease and it remains in the envelope causing deformation of the nucleus. Because the RSYLLG sequence is deleted from the gene for lamin A, the COOH3 portion of the gene remains attached, holding lamin A to the nuclear envelope. There are some types of treatments for this disease now.

myosin I

present in all types of cells. Myosin I has a head domain (that binds to an actin filament) and a tail (which varies but determines the type of cargo the myosin drags along). myosin can be bound to vesicles or the the plasma membrane. myosin I has a single head and contributes to vesicle movement through the cell. It is also often bound to the plasma membrane to change the arrangement of actin filaments. primarily motor domain with about 300 additional amino acids. single line structure.

intermediate filament structure

rope-like made of intermediate filament proteins, fibrous subunits (central rod domain and unstructured ends) the subunits form dimers which then join with another dimer running in the opposite direction to form a tetrameter. formation begins with NH2 to COOH monomer that runs parallel to another monomer to form a coiled-coil. Then forms a tetrameter with an antiparallel dimer. Tetramers come together in a group of 8. cells would rupture without intermediate filaments because it loses flexibility.

sarcoplasmic reticulum

same thing as ER triad refers to orientation of sarcoplasmic reticulum to T tubule to sarcoplasmic reticulum.

stathmin

similar to profilin/thymosin binds subunits of microtubules and prevents assembly. stathmin binds the building blocks. It has two binding sites (one for each dimer). GTP hydrolysis will eventually catch up.

protofilaments

single protofilaments are unstable because they could break at any point within. when multiple protofilaments are joined in rows, they are thermally stable. more stable than just a single line of microtubule

striated muscle

skeletal muscle is also known as striated muscle because of the orientation of actin and myosin in the sarcomeres.

melanocyte/melanosome

skin pigments that have motor proteins that move the pigments in or out based on their exposure goal. The vesicle is melanosome (melanin). These cells are known as melanocytes.

cell cortex

specialized layer of cytoplasm on the inner face of the plasma membrane. In animal cells, it is rich in the actin filaments that govern cell shape and drive cell movement. actin filaments are linked by actin-binding proteins in a meshwork that supports the plasma membrane and gives it mechanical strength. many actin filaments are linked to the cell cortex with actin-binding proteins. actin-binding proteins cross-link actin filaments together in a gel-like meshwork within the cell cortex.

Ca++

stored in sarcoplasmic reticulum. The release of Ca++ is regulated for muscle movement.

focal contact

stress fibers are anchored at focal adhesions. Focal adhesions allow interaction between actin inside the cell and things outside. Focal contacts help a cell move with traction forces.

myosin II

structure: individual myosin molecules are formed by two coiled-coil alpha helices that have a head domain and a tail. A myosin II filament is formed when many molecules join with tails facing and heads at opposite ends. muscle myosin belongs to this family. All of which as dimers, with two globular ATPase heads at one end and a single coiled-coil at the other. when clusters of myosin II molecules bind to each other, forming a bipolar myosin filament, it can pull actin filaments in either direction. myosin II has 2 essential, 2 regulatory, and 2 heavy sections for 6 total protein units. muscle is the best/most famous way that actin and myosin have been studied. Myosin II forms a coiled-coil tail and two heads. and an extended blank zone of additional amino acids. Together myosin filaments are formed by a bipolar filament with heads on either end and a bare zone in the center. With actin filaments attached to either end, they will walk along the actin in opposite directions and causes actin filaments to slide past each other to contract.

synthesis by polymerization

subunits that come together to create a filamentous polymer

actin filaments

thin, flexible protein filament made from a chain of globular actin molecules; a major component of all eukaryotic cells, this cytoskeletal element is essential for cell movement and for the contraction of muscle cells. helical structure globular actin twist together "pointing" in the same direction actin filaments are usually thinner, more flexible and shorter than microtubules. they are generally found in cross-linked bundles and networks which are much stronger than individual filaments. actin filaments polymerize similarly to microtubules. A naked actin filament can disassemble from either end. the actin monomer is compared to like a clamshell with an ATP binding site. They have a plus end (rapid growth) and a minus end (slower growth). about 5% of the total protein in animal cells is actin (half as monomers and half as filaments) 7nm actin filaments allow animal cells to adopt to a variety of shapes and perform a variety of functions a) microvilli b) contractile bundles in the cytoplasm c)fingerlike filopodia protruding from the leading edge of a moving cell d) contractile ring during cell division

lamellipodia extension

this cell begins spread over its surface. actin is polymerized at their plus ends to protrude the front end of the lamellipodium. at the back end, myosin motor proteins slide actin filaments forward. at the front end, focal contracts (with inegrin) form with the surface. the actin forms many branched structures to extend forward. capping proteins are added the the actin filaments in the middle of the branching to prevent their break down. cofilin is integrated at the back end to encourage twisting of the actin filaments and leads to their breakdown, releasing actin monomers.

pericentriolar matrix

this is the zone where the gamma tubulin ring complex localize, nucleation sites for microtubules. no microtubules extend directly from the triplet of microtubules that make up the centrioles.

Acytylcholine for in neuotransmitters

travels through neuotransmitters to cause action potential at the neuromuscular junction to cause voltage gated calcium channels to open.

formin

type of actin-binding protein that nucleates assembly and remains associated with the growing plus end.

myosin

type of motor protein that uses ATP to drive movements along actin filaments. the motor domain is the head amino terminal end while the C terminal end is opposite. one subtype interacts with actin to form the thick contractile bundles of skeletal muscle. all actin-dependent motor proteins belong to the myosin family. moves toward the plus end. myosin and other acting-binding proteins can regulate the location, organization and behavior of actin filaments. All of this is controlled by extracellular signals. large family of actin binding proteins that act like motors by the hydrolysis of ATP and moves toward the plus end. myosin V is much faster than myosin II. myosin V has two longer heads and a blank zone in the middle with more amino acids on the other end.

treadmilling

when dimers are added to the plus end but lost at the minus end at the same rate. when actin is lost and added to the plus and minus ends at the same rate so there is no growth or shrinkage. when the concentration of GTP-tubulin is less than GDP-tubulin there is shrinkage.

GTP cap

when there are many GTP-bound dimer on the end of a microtubule filament. important form maintaining stability. If the end is hydrolyzed too quickly it will become unstable. once the GTP cap is lost, the microtubule is unstable and undergoes catastrophe cells will undergo a constant growth (rescue) and shrinkage (catastrophe).

nebulin

yardstick protein that binds lengthwise to actin in sarcomeres.